Impact of Diluents on Flame Stability With Blends of Natural Gas and Hydrogen

Two potential decarbonization pathways for natural gas (NG)-fueled gas turbine engines include blending hydrogen (H₂) into NG and postcombustion carbon capture. H₂ blending changes several combustion properties, including flame speed and stretch sensitivity. The use of post-combustion carbon capture systems is typically facilitated by the implementation of exhaust gas recirculation (EGR), where exhaust gases are injected into the inlet of the engine, increasing carbon dioxide (CO₂) concentration at the outlet and, hence, increasing the efficiency of carbon capture technologies. In this work, we explore the impact of H₂ blending and EGR on the stability of a swirl-stabilized, central-piloted flame. Mixtures of NG and H₂ are tested at a range of different diluent compositions, with oxygen varied from 21% to 15% by volume in the oxidizer. In all cases, a constant adiabatic flame temperature is maintained to mimic the operation of a gas turbine at a given turbine inlet temperature. A variable-length combustor is used for testing, where combustor length is varied to understand the dynamic stability characteristics of the system. Results show that EGR and H₂ work in opposition to each other, where higher levels of EGR result in poor flame holding and higher levels of H₂ result in better flame holding. Increasing H₂ generally increases the amplitude of thermoacoustic instability at each condition, a result of the change in flame position in this particular combustor. Importantly, H₂ can be added to NG to improve flame holding without significantly decreasing CO₂ levels in the products, showing that H₂ blending can be a method for counteracting combustor operability issues that arise from high levels of EGR necessary to improve the efficiency of typical carbon capture systems.